The present invention is directed to a fastening element assembly for use in a hard receiving material, such as concrete, masonry and the like, and includes a sleeve and a bolt. The bolt has a pointed tip at the leading end of a shank extending toward the trailing end. The shank has an axial length greater than that of the sleeve. Further, the shank has an outside shape corresponding at least in part to an inside shape of the sleeve.
At the present time, apart from installation by drilling, so-called direct installation is used for securing fastening elements in hard and brittle receiving materials, such concrete, masonry and the like. In direct installation, a nail-like fastening element is driven directly into the receiving material by an explosive powder charge operated setting tool without any prior drilling of the receiving material. When it is driven in, the fastening element causes a displacement of the receiving material in the region of its insertion. Very high compressive stresses develop in the receiving material due to its displacement when the fastening element is driven in, producing spalling at the surface of the receiving material. Such spalling is not only aesthetically undesirable, but it also results in a considerable reduction in the anchoring value of the fastening element.
To avoid spalling and associated failure of a fastening element anchorage, it is known from DE-PS 28 49 139 corresponding to U.S. Pat. No. 4,287,656, to drill a borehole in the receiving material prior to driving the fastening element, with the borehole having a diameter slightly larger than the diameter of the shank of the fastening element and with a length at least twice its diameter. After the borehole is formed, the fastening element is driven through the base of the borehole. As a result, maximum compression stresses are displaced from the surface of the receiving material to a location inwardly of the surface. Accordingly, the spalling, as mentioned above, can be avoided. Apart from the separate drilling tool, needed for forming a borehole for the fastening element, it has also been known to shape the leading end of the fastener as a drilling or cutting edge, whereby the fastening element can cut its own borehole. Such an arrangement is quite costly, in part, because of the use of hard metal cutting plates or the like.
In a procedure set forth in U.S. Pat. No. 3,480,306, a cylindrical sleeve is inserted into a previously formed borehole and, subsequently, a fastening element is driven into the sleeve. The sleeve is widened radially and expanded into the borehole due to the driving of the fastening element. The tip of the fastening element can penetrate into the receiving material through the base of the borehole for a greater or lesser depth. This procedure requires a relatively high expenditure of time for fabrication of the borehole.